PVD coated cutting tools where a PVD coating is deposited on a cemented carbide substrate are well known in the art.
Nanolayered PVD coatings composed of a multiple of sublayers of different compositions have been used since a long time. These coatings are made of different sublayers A, B, C . . . commonly being metal nitrides that have been repeatedly deposited in a manner, e.g., A/B/A/B/A . . . or A/B/C/A/B/C/A . . . . The individual sublayers normally have a thickness of between 3 and 100 nm, many times between 5 and 25 nm which means that the total number of sublayers for each micrometer thickness of the nanolayered PVD coating are large. The metals may belong to groups 4, 5 and 6 in the periodic table of elements such as Ti, Zr, V, and Cr, commonly also together with Al and Si. Specific examples are for example nanolayered coatings where the individual layers are TiAlN and TiN, or different TiAlN sublayers having different Ti/Al ratios.
Cemented carbide substrates in cutting tools may have various contents of binder phase, normally Co. Beside the main component WC, other hard constituents such as carbides of Ti, Ta and Nb may in some cases also be present. Additions of elements like Cr may also have been made. The specific combination of components in the cemented carbide, as well as the specific sintering process, gives the actual microstructure and affects properties such as toughness and hardness.
Milling of steel is an important metal cutting operation in the industry. ISO P materials are in particular widely used. Milling operations are demanding metal cutting operations which are typically intermittent in nature. The thermal and mechanical load will vary over time. The former induces thermal tensions which may lead to so-called thermal cracks in the coatings, while the later may cause chipping in the cutting edge due to fatigue. Thus, common wear types in milling are cracking and chipping, i.e., small fragments of the cutting edge loosening from the rest of the substrate. Both may be enhanced should flaking of the coating at an early stage. Increasing the thermal crack resistance, edge toughness and flaking resistance are thus of great importance to increase tool lifetime. PVD coatings are commonly used in cutting tools for milling operations. The use of a nanolayered PVD coating in general instead of a homogeneous PVD coating may reduce the propagation of cracks through a coating. Also, a nanolayered coating specifically comprising harder sublayers interlaid with softer sublayers may further reduce the risk of chipping through shock absorption by the softer sublayers.
For milling applications of ISO P steels there is thus a need for a coated cutting tool which shows an overall combination of good edge line toughness (resistance to chipping in the edge line), good thermal crack resistance, good flaking resistance and good chemical and abrasive wear resistance.
In contrast to milling, turning is a continuous machining operation. Heat resistant super alloys (HRSA) and titanium, i.e., ISO S materials, are important materials in. e.g. the aerospace industry. Machining ISO S materials is challenging due to the properties of the workpiece material. These materials are hard and smearing. Machining them generate a lot of heat and promote wear mechanisms such as adhesive, abrasive and chemical wear. Notch formation, flaking and chipping are common reasons for reaching tool life. For turning applications of ISO S materials there is thus a need for a coated cutting tool which shows an overall combination of good edge line toughness (resistance to chipping in the edge line), abrasive and chemical wear resistance and good flaking resistance. Thanks to their toughness, and hot hardness, nanocristalline high Al content PVD coatings are extensively used for machining ISO S materials.
EP 1 795 628 A1 discloses a coated cutting tool for milling of steel alloys and stainless steels where a cemented carbide substrate containing 8-11 wt % Co and 0.1-0.5 wt % Cr is coated with a nanolayered PVD coating A/B/A/B/A . . . wherein the sublayers A and B consists of AlxTi1-xN and TiyAl1-yN, x=0.4-0.7 and y=0.6-1, x<y.
EP 2 011 894 A1 discloses a coated cutting tool insert for parting, grooving and threading of steel and stainless steels comprising a cemented carbide substrate and a PVD coating comprising two (Ti,Al)N-layers with different Ti/Al ratios. In one embodiment the PVD coating is made of an inner aperiodic TiAlN lamella coating consisting of alternating layers of AlzTi1-zN and AlvTi1-vN where z=0.55-0.70 and v=0.35-0.53 and an outer (Ti,Al)N lamella coating consisting of alternating layers of AlmTi1-mN and AlnTi1-nN and AlkTi1-kN where m=0-0.1, n=0.35-0.53 and k=0.55-0.70. The cemented carbide substrate comprises 7.5-10.5 wt % Co and 0.8-1.0 wt % Cr.
EP 2 008 743 A1 discloses a coated cutting tool insert for turning in heat resistant superalloys and stainless steels comprising a cemented carbide substrate and a PVD coating comprising an aperiodic (Ti,Al)N lamella coating with an average composition of 0.4-0.7. The individual lamellas have a composition AlxTi1-xN, where x=0.4-0.7, and TiyAl1-yN, where y=0.6-1. The cemented carbide substrate comprises 5-8 wt % Co and 0.3-1.5 wt % Cr.